The T-lymphocyte lung disorders occur in 20 to 50 per 100,000 of the U.S.A population. The "model" disorder of this group is sarcoidosis, a disease characterized by the accumulation of activated helper T-lymphocytes at the sites of disease. These T-cells spontaneously express the interleukin-2 gene, thus driving T-cells in the local milieu to proliferate. Treatment of these individuals with corticosteroids results in suppression of interleukin-2 gene expression, cessation of lung T-cell proliferation, and improvement in lung function.